There exist a variety of fabrics today which are capable of acting as a barrier to particulate matter, water and other liquids yet which allow water vapor and air to pass therethrough. Such fabrics are commonly referred to as "breathable barriers." Breathable barrier fabrics have been employed in outdoor fabrics, tarpaulins, garments, personal care products, infection control products, as well as numerous other articles. Moreover breathable barrier fabrics are often preferred over non-breathable barrier materials since breathable barrier fabrics allow moisture trapped beneath the fabric to escape as water vapor. Thus, apparel using breathable barriers are generally more comfortable to wear since the migration of water vapor through the fabric helps to reduce and/or eliminate discomfort resulting from excess moisture trapped against the skin.
While a variety of breathable barrier fabrics are known in the art, one particularly useful breathable barrier comprises stretched-filled microporous films. Such films are typically filled with particles and then crushed or stretched to form a fine pore network throughout the film. The fine pore network allows gas and water vapor to pass through the film while acting as a barrier to liquids or particulate matter. The amount and size of filler within the film and the degree of stretching is controlled so as to create a network of micropores which are of a size and frequency to impart the desired level of breathability to the fabric. For example, U.S. Pat. No. 4,777,073 issued to Sheth discloses a breathable polyolefin film filled with about 15 to 35% by volume calcium carbonate and stretched to about four times its original length. Similarly, U.S. Pat. No. 5,169,712 issued to Tapp discloses an oriented porous film comprising ethylene-propylene block copolymers filled with a nucleating agent and calcium carbonate which may be stretched up to about seven times its original length in order to create a breathable microporous film.
While filled microporous films are capable of providing articles with good barrier properties and breathability, efficient commercialization and practical applications of such films requires improved stretch, strength and toleration of defects. In this regard, stretching or down-gauging of filled films often makes them particularly susceptible to irregularities such as, for example, pinholes, gels larger than the film thickness, particulate contamination and/or uneven polymer distribution. While not detracting from film breathability, the barrier properties of stretched-filled films may be compromised since these irregularities tend to create defects (i.e. macroscopic holes) or zones of weakness in the film. This is of enormous concern where the film is intended to act as a barrier to urine, blood or other bodily fluids and pathogens associated therewith. Moreover, stretching of the filled films to the required degree, while acting to orient the film and also make the film microporous, has the adverse effect of reducing the strength and elongation of the resulting breathable film. In light of the many uses of such films, particularly in garments or infection control products, a breathable barrier fabric with improved durability is highly desirable since films of lesser strength will tend to tear more readily and also be more restrictive to movement.
Thus, there exists a need for improved filled microporous films and particularly such films having improved strength and stretch characteristics. Moreover, there exists a need for filled films which have reduced levels of and/or which are more tolerant of these irregularities when stretched. Further, there exists a need for a method of making such stretched-filled films and, in particular, a method of making a breathable film which improves the physical characteristics of the resulting film and/or reduces the potential for film defects.